G/U Modular +1/1 infinite combo (Modern)

Devoted Druid + Quillspike = infinite +3/3 on Quillspike
Devoted Druid + Leech Bonder + Paradise Mantle = infinite green mana and infinite -1/1 on opponent's creatures
Devoted Druid + Leech Bonder + Paradise Mantle + Protean Hydra/Primordial Hydra = infinite green mana, infinite +1/1 on your creatures and infinite -1/1 on opponent's creatures
Leech Bonder + Paradise Mantle + 2/2 Protean Hydra = infinite +1/1 on Protean Hydra at next end step
Hardened Scales + Leech Bonder + Paradise Mantle = infinite +1/1 on all your creatures
Training Grounds + Gilder Bairn + Paradise Mantle = infinite +1/1 on all your creatures
Training Grounds + Gilder Bairn + Paradise Mantle + Leech Bonder + Paradise Mantle = infinite +1/1 on all your creatures and infinite -1/1 on opponents creatures
Training Grounds + Paradise Mantle + Umbral Mantle + Creature = infinite +2/2 on that creature
Training Grounds + Paradise Mantle + Umbral Mantle + Vault Skirge = infinite +2/2 on Vault Skirge and infinite life for you if you deal damage
Leech Bonder + Paradise Mantle = infinite ability to move counters

Note 1: once you get infinite +1/1 you can also have infinite turns with Sage of Hours.
Note 2: if you can't get infinite counter quickly you can use lands, Devoted Druid and Paradise Mantle to get enough mana to cast Howlgeist. Keep it without counters until you get a certain quantity of +1/1; if it dies, just return it to the battlefield and move its +1/1 counter to another creature. When you can produce enough +1/1 give them to Howlgeist and attack.